Transcript Lecture8.0 Silicon Crystal Growth.ppt

Lecture 8.0
Silicon Crystal Growth
Silicon Mfg. - old
Produce Silicon metal bar
 Zone Refining – n times

– To get purity
Cut off impure end
 Use pieces to fill crystallization
apparatus
 Grow Mono-Crystal of large size

Zone Refining
0=x-Ut, k=CS/CL
Co=solute concentration in melt
or of solid on first pass
Co=0x+L Cs(x)dx - ox-L kCL(x)dx
Si-Fe Phase Diagram
Si-O Phase Diagram
Crystal Growth
Silicon Mfg. - new
Produce ultra pure Silicon cylinder
 Use pieces to fill crystallization
apparatus
 Grow Mono-Crystal of large size

Add Dopants to
Silicon Grown

Melt is maintained
with a given
impurity
concentration
 Melting Point is
decreased
 Solid produced
has a given
impurity
concentation
Ultra-pure Silicon Production

Si + 3HClSiHCl3 +H2
– fluidized bed reactor at 500 to 700K
– Condense chlorosilane, SiHCl3

Distillation of liquid SiHCl3
 SiHCl3+H2Si + 3HCl at 1400K
 Si vapor Deposits on Si mandrel in a
purged fed batch reactor heated to 700K
 Results Large diameter Si with impurities
at 10 ppt or 14-9’s pure
12” (30 cm) Boule
Crystal Growth
Czochralski Crystal Growth
Apparatus

Figure 4. Today's Czochralski growth furnace,
or crystal puller, is a far more sophisticated
apparatus than that built by Gordon Teal
nearly 50 years ago. It is however
fundamentally identical. A crystal is pulled
from a feedstock of molten material by slowly
withdrawing it from the melt. Czochralski
pullers often possess provisions for adding to
the melt during a single pull so that crystals
larger than what can be obtained in a single
charge of the crucible may be produced. Today
crystals of a 12-inch diameter are possible,
and the industry will spend billions to adopt
this new size in the coming years. This figure
was taken directly from the Mitsubishi
Semiconductor
–
website: http://www.egg.orjp/MSIL/
english/index-e.html!
Czochralski Growing System
12” (30 cm) Boule
Crystal Growth Steps

Induce Supersaturation
– Sub cooled melt
– S=exp[THf/(RT2)dT]
Nucleation
 Growth at different rates on each
Crystal Face
 Results in crystal with a particular
Crystal Habit or shape

Nucleation

Free Energy
– GTOT=Gv V + A

Critical Size
– R*=2AVm/(3vRgT lnS)

Nucleation Rate

J=(2D/d5)exp[- G(R*)/(RgT)]

D=diffusion coefficient
 d= molecular diameter
Surface Nucleation
Surface energy, ,
is replaced by  cos
, where  is the
contact angle
between phases
 Geometric factors
changed
 Units #/(cm2sec)
 Surface Nucleation

– Limits growth of flat
crystal surfaces
Crystal Growth

Boundary Layer
Diffusion
 Surface Diffusion
 Edge Diffusion
 Kink Site
Adsorption

Loss of
Coordination
shell at each step
Crystal Growth Rate
Limiting Steps



Boundary Layer
Diffusion
Surface Diffusion
Surface Nucleation
– Mono
– Poly

Screw Disslocation
 Edge Diffusion
 Kink Site Adsorption
 Loss of Coordination
shell
Screw Surface Growth
Fluxes
Boundary
Layer
 Surface
 Edge

Mass Transfer to Rotating Crystal

Local BL-MT Flux

J[mole/(cm2s)] = 0.62 D2/3(Co-Ceq) n-1/6 w1/2
J[mole/(cm2s)] = 0.62 D2/3 Ceq(S-1) n-1/6
w1/2

–
Franklin, T.C. Nodimele, R., Adenniyi, W.K. and Hunt,
D., J. Electrochemical Soc. 135,1944-47(1988).
– Uniform, not a function of radius!!

Crystal Growth Rate due to BL-MT as
Rate Determining Step
Heat Transfer to Rotating Crystal

Local BL-HT Flux

J[mole/(cm2s)] = h(Teq-T)/Hf
J[mole/(cm2s)]
• = 0.62 k -1/3 n-1/6 w1/2 (Teq-T)/Hf

–
Franklin, T.C. Nodimele, R., Adenniyi, W.K. and Hunt,
D., J. Electrochemical Soc. 135,1944-47(1988).
– Uniform, not a function of radius!!

Crystal Growth Rate due to BL-HT as
Rate Determining Step
Crystal Habit

Equilibrium Shape
– h1/1=h2/2=h3/3

Kinetic Shape
– h1=G1(S)*t
– h2=G2 (S)* t
– h3=G3 (S)* t
Crystal Faces

Flat Face
 Stepped Face
 Kinked Face

Diffusion Distances
to Kink sites are
shorter on K &S
Faces
Crystal Habit
Wafers Cut from Boule & Polished